DE102017123815B4 - INVERTER AND METHOD FOR OPERATING AN INVERTER - Google Patents

Abstract

Inverter (1) with a bridge circuit (2) which has two half bridges, each with two semiconductor switches connected in series, wherein the end points of the series circuits are each connected to direct current connections (4) of an input-side intermediate circuit capacitance (3) and the center points of the series circuits are connected to output lines (5a, 5b) for connection to an alternating voltage network, wherein the output lines (5a, 5b) are each connected to one of the end points of the series circuit via a discharge path (9a, 9b) comprising a filter capacitance (8), and wherein the inverter (1) has a control unit (10) which is designed to generate a clocked control of the semiconductor switches of the bridge circuit (2) depending on an alternating current measured on the output side of the bridge circuit (2), wherein the control unit (10) is connected to at least one current sensor (11a, 11b, 12, 14, 15, 17, 18, 19, 20, 22, 23) for measuring the alternating current, characterized in that the alternating current measured on the output side of the bridge circuit (2) is detected at at least two measuring points (13a, 13b, 16a, 16b, 16c, 21), wherein a first measuring point (13a, 13b, 21) is arranged in one of the output lines (5a, 5b) and a second measuring point (16a, 16b, 16c) is arranged in one of the discharge paths (9a, 9b) or in a common return line (9c) to the end point of the series connection, wherein a measuring point (13a, 13b, 21) for measuring a mains frequency portion of the alternating current is arranged in only one of the output lines (5a, 5b), while the other output line (5a, 5b) is free of measuring points (13a, 13b, 21) for measuring alternating current.

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to an inverter and a method for operating an inverter which converts an input-side direct current into an output-side alternating current for feeding into an alternating voltage network.

STATE OF THE ART

From the US 9 712 082 B2 An inverter with at least two output lines for connection to an alternating voltage network is known, in which a current sensor is connected to the output lines and generates a measurement signal depending on the sum of the alternating currents flowing in the output lines. In a corresponding method, this measurement signal is used to control an inverter bridge circuit of the inverter in that the measurement signal contains a first high-frequency component of the alternating current that flows in a first of the output lines during a half-wave of an alternating current fed into the alternating voltage network, and a second high-frequency component of the alternating current that flows in a second output line during a second half-wave. The current sensor is constructed in such a way that the flow directions of the respective alternating current in the output lines at the input of the current sensor are identical, so that the current sensor outputs a structurally superimposed sum signal.

From the US 2012 / 0 063 179 A1 A three-phase inverter is known in which alternating currents are measured in each of the three output lines and in each of the discharge paths assigned to the output lines.

TASK OF THE INVENTION

The invention is based on the object of providing an inverter and a method for operating an inverter with a simple and cost-effective current sensor system for detecting mains frequency and high frequency components of an output-side alternating current.

SOLUTION

The object is achieved by an inverter having the features of patent claim 1 and by a method for operating an inverter having the features of patent claim 11. Preferred embodiments are defined in the dependent patent claims.

DESCRIPTION OF THE INVENTION

An inverter according to the invention comprises a bridge circuit which has two half bridges, each with two semiconductor switches connected in series, the end points of the series circuits being connected to direct current connections of an input-side intermediate circuit capacitance. The midpoints of the series circuits of this so-called H4 bridge are connected to output lines for connection to an alternating voltage network. The output lines are each connected to one of the end points of the series circuit via a discharge path comprising a filter capacitance. The inverter has a control unit which is set up to generate a clocked control of the semiconductor switches of the bridge circuit depending on an alternating current measured on the output side of the bridge circuit. For this purpose, the control unit is connected to at least one current sensor arranged on the output side of the bridge circuit for measuring the alternating current on the output side.

The inverter is characterized in that the alternating current measured on the output side of the bridge circuit is detected at at least two measuring points, wherein a first measuring point is arranged in one of the output lines and a second measuring point is arranged in one of the discharge paths or in a common return line to the end point of the series connection.

The invention is based on the finding that a measurement of the high-frequency component of the alternating current is possible not only in the output lines, but also in the discharge paths, whereby the return line can be regarded as a common part of the discharge paths. This finding makes it possible to use a measuring sensor system that is optimally designed for the first measuring point or the second measuring point and their respective properties and boundary conditions. In particular, it is sufficient to arrange a measuring point in only one of the output lines, so that a second measuring point in the other output line can be avoided and in particular the other output line can be arranged more flexibly in terms of space.

In one embodiment of the inverter, the first measuring point is arranged in one of the output lines and the second measuring point is arranged in the discharge path connected to the other output line. The mains frequency component of the alternating current and the high frequency component of the alternating current in one of the output lines are measured at the first measuring point, while the high frequency components of the alternating current in the other output line are measured at the second measuring point. recorded. The mains frequency component recorded at the first measuring point is essentially identical in both output lines and is used in the control unit to regulate, for example, the output power of the inverter. The high-frequency components of the alternating current used by the control unit to regulate, for example, the optimal sinusoidal course of the alternating current are composed of the high-frequency components of the current recorded at the first measuring point in one of the output lines and the high-frequency components of the current recorded at the second measuring point in the discharge path connected to the other output line. This means that all high-frequency components required for regulation are recorded, even if they only flow in one output line or in the other output line, at least temporarily.

In a further embodiment of the inverter, the current sensor is designed to detect a superimposed sum signal of the currents flowing at the first measuring point and the currents flowing at the second measuring point. This means that all relevant components of the alternating current can be detected with a single sensor and sent to the control unit. The sensor can be designed as a conventional current transformer with or without a toroidal core, whereby the measuring points can be formed by passing one of the output lines and a discharge path or the return line through the current transformer. A known current sensor through which both output lines are routed has the disadvantage compared to this configuration that the mains frequency component flowing in both output lines is structurally added together and the current sensor must therefore be designed for double amplitude. This does not apply to the high-frequency components of the alternating current with a comparatively small amplitude, since these regularly flow exclusively in one of the output lines, so that the current sensor according to this embodiment has to cover a smaller dynamic range and can be built accordingly more compactly and inexpensively. In addition, the return line or the discharge path can be routed through the current transformer several times to increase the sensitivity of the current sensor for the high-frequency components of the alternating current.

The current sensor can also be set up to record a combination of measured values of the currents flowing at the first measuring point, at the second measuring point and at a third measuring point, with the second measuring point being arranged in one of the discharge paths and the third measuring point in the other discharge path. For this purpose, the discharge paths can be led through a common current transformer so that the currents flowing in both discharge paths are recorded. In particular, by appropriately selecting the direction in which the individual lines are fed through the current sensor, a constructive summation of these currents can be set up, which enables optimal recording of the mains frequency component and the high frequency components of the alternating current.

In a further embodiment, the inverter comprises a first current sensor and a second current sensor, wherein the first current sensor detects a current flowing at the first measuring point and the second current sensor detects a current flowing at the second measuring point. The second current sensor can be optimized for measuring the high-frequency components of the alternating current with a comparatively small amplitude flowing at the second measuring point, i.e. in the discharge path or in the return line, and is thus in particular more compact and less expensive than another current sensor arranged in the other output line.

In a further embodiment of the inverter, the second current sensor is designed to detect a superimposed sum signal of the currents flowing at the second measuring point and at a third measuring point, with the second measuring point being arranged in one of the discharge paths and the third measuring point being arranged in the other discharge path. As a result, the second current sensor can detect all high-frequency components of the alternating current, and the first current sensor can be optimized for measuring the mains frequency component, i.e. in particular with a smaller dynamic range and can be designed more cost-effectively.

The current sensors of the embodiments of the inverter according to the invention can be designed as magnetic current transformers. This is particularly advantageous if the current sensor comprises several measuring points in that several lines can be passed through it. Alternatively, a current sensor can comprise several sub-sensors at different measuring points, the measuring signals of which can be linked together in analog form, for example by means of operational amplifiers, or digitally in a processor.

In one embodiment of the inverter, the second current sensor comprises a shunt resistor for measuring current. This is possible because the second current sensor only detects high-frequency components of the alternating current. By arranging the second current sensor in the discharge path or in the return line, the ohmic resistance of the shunt resistor does not cause any efficiency losses and therefore does not have to be laboriously minimized.

In a further embodiment of the inverter, a shunt resistor is arranged in each of the two discharge paths, and voltages at the shunt resistors are combined by means of a differential amplifier to form an output signal of the second current sensor. This makes it particularly easy for the second current sensor to detect all high-frequency components of the alternating current and to pass them on to the control unit as a single superimposed sum signal, and the first current sensor can be optimized for measuring the mains frequency component.

In a preferred embodiment of the inverter, the first measuring point is arranged at a position in one of the output lines on the side of the connection point of the respective discharge path with this output line facing away from the bridge circuit. This makes it possible to avoid having to arrange a measuring point or a corresponding voluminous current sensor at a position along the output lines that lies within the current paths for the high-frequency components, so that this current path from the center points of the series connections of the bridge circuit via the output lines, the discharge paths and the return line to the end point of the series connections can be minimized much better, which, among other things, contributes to improving the electromagnetic compatibility of the inverter. In addition, the second measuring point can be arranged in the return line or a second current sensor with two measuring points can be arranged in the discharge paths, so that two sensors are required to record the entire alternating current, one of which can be optimized for measuring a mains frequency component and the other for measuring high-frequency components.

A method according to the invention for operating an inverter according to one of the preceding embodiments is characterized in that the semiconductor switches of the bridge circuit are controlled by means of a unipolar clock, wherein the alternating current flowing on the output side of the bridge circuit is detected at at least two measuring points, wherein a first measuring point is arranged in one of the output lines and a second measuring point is arranged in one of the discharge paths or in the return line.

In one embodiment of the method, a mains frequency component of the alternating current is measured at the first measuring point and high frequency components of the alternating current are measured at the second measuring point. The measured values recorded at the first measuring point and those recorded at the second measuring point can be transmitted separately to the control system.

In a further embodiment of the method, the measured values recorded at the first measuring point include the mains frequency component of the alternating current and high-frequency components of the alternating current in one half-wave of the alternating current, and the measured values recorded at the second measuring point include high-frequency components of the alternating current in the other half-wave of the alternating current. Alternatively, the measured values recorded at the first measuring point include exclusively the mains frequency component of the alternating current, and the measured values recorded at the second measuring point include high-frequency components of the alternating current in both half-waves of the alternating current.

In a further embodiment of the method, the measured values recorded at the first measuring point by the first current sensor include exclusively the mains frequency component of the alternating current, and a second current sensor records the high frequency components of the alternating current flowing via the discharge paths and transmits these to the control system. Alternatively, the currents flowing at the first measuring point, at the second measuring point and, if applicable, at the third measuring point can be recorded by means of a common current sensor and transmitted to the control system as a superimposed sum signal.

BRIEF DESCRIPTION OF THE CHARACTERS

• 1a, 1b zeigen aus dem Stand der Technik bekannte Wechselrichter und
• 2-5 zeigen verschiedene Ausführungsformen erfindungsgemäßer Wechselrichter.

In the following, the invention is further explained and described with reference to embodiments shown in the figures.

• 1a , 1b show state-of-the-art inverters and
• 2-5 show various embodiments of inverters according to the invention.

FIGURE DESCRIPTION

1a shows a conventional inverter 1 with a bridge circuit 2, which has two half bridges, each with two semiconductor switches connected in series. The end points of the series circuits are connected to an input-side intermediate circuit capacitance 3 and to direct current connections 4 for connecting a direct current generator, for example a photovoltaic generator, or a battery. The center points of the series circuits are connected to output lines 5a, 5b, which end in alternating voltage connections 5 for connecting the inverter 1 to an alternating voltage network. Filter inductances 6 and an output filter 7 with further inductances and capacitances are arranged between the bridge circuit 2 and the alternating voltage connections 5.

The output lines 5a, 5b of the inverter 1 are each connected via a discharge path 9a, 9b comprising a filter capacitance 8 to a common return line 9c to one of the end points of the series connection.

The inverter 1 comprises a control unit 10, which is connected to the semiconductor switches of the bridge circuit 2 and controls the bridge switches by means of clocked control signals. The control signals can in particular follow a unipolar or bipolar clock pattern generated in a known manner, which is generated for example by a PWM controller and is suitable for generating a sinusoidal output current with a mains frequency of the AC voltage network at the AC voltage connections 5 by means of the bridge circuit 2.

During operation of the inverter 1, in particular due to the clocking of the semiconductor switches of the bridge circuit 2 in the kHz range, high-frequency components arise in the alternating current in the output lines 5a, 5b, which are partially attenuated by the filter inductances 6 and partially flow via the discharge paths 9a, 9b and the return line 9c to one of the end points of the series connections of the bridge circuit. These high-frequency components are superimposed on the actually desired sinusoidal output current of the bridge circuit 2.

The control unit 10 is connected to two current sensors 11a, 11b, which are arranged in the output lines 5a, 5b between the respective filter inductance 6 and the respective connection point of the discharge paths 9a, 9b with the output lines 5a, 5b. The current sensors 11a, 11b can have various known designs and can include, for example, shunt resistors or current transformers with or without a toroidal core.

The control unit 10 processes the measurement signals of the current sensors 11a, 11b both with regard to the mains frequency component of the alternating current in the output lines 5a, 5b, which is used in particular to regulate the output power of the inverter 1, and with regard to the high-frequency components of the alternating current. The high-frequency components are evaluated in particular with regard to interference with frequencies in the range between the mains frequency and the clock frequency and are used as part of a control system to minimize these interferences by appropriately modifying the clocking of the semiconductor switches of the bridge circuit 2.

The mains frequency component of the alternating current of the inverter 1 flows in opposite directions through the output lines 5a, 5b, whereby the mains frequency components of the currents in the output lines 5a, 5b have largely identical amplitudes, so that one of the current sensors 11a, 11b would be sufficient to determine the mains frequency component of the alternating current. In order to correctly determine the high frequency components of the alternating current, however, it is necessary to consider the currents flowing in the individual output lines 5a, 5b separately, since the high frequency components flow only in the first output line 5a or only in the second output line 5b, depending on which of the semiconductor switches of the bridge circuit 2 is clocked at a time, and accordingly only via the respective discharge path 9a or 9b to the end point of the series circuits of the bridge circuit 2.

1b shows another known inverter 1, which instead of the two current sensors 11a and 11b according to 1a only one current sensor 12 covering two measuring points 13a, 13b which are located at the same positions as the current sensors 11a, 11b according to 1a The output lines 5a, 5b are guided through the current sensor 12 in such a way that the current sensor 12 detects the currents flowing at the measuring points 13a, 13b, and the output lines 5a, 5b are oriented to the current sensor 12 in such a way that the flow directions of the mains frequency portion of the alternating current in the output lines 5a, 5b at the input of the current sensor 12 are identical. As a result, the current sensor 12 can detect a structurally superimposed sum signal of the mains frequency portion of the currents at the measuring points 13a and 13b and output a measurement signal that represents the mains frequency portion of the alternating current with doubled amplitude. In addition, the current sensor 12 measures and sums according to 1b the high-frequency components of the currents in the output lines 5a, 5b, so that the high-frequency components of the alternating current are always represented in the measurement signal output by the current sensor 12, even if these high-frequency components only flow in a single one of the output lines 5a, 5b.

2a shows an inverter 1 according to the invention with a first current sensor 11b in the second output line 5b and a second current sensor 14 in the return line 9c. The first current sensor 11b detects the mains frequency component of the alternating current as well as the high frequency component of the alternating current in the second output line 5b in which it is arranged. However, the first current sensor 11b cannot detect high frequency components of the alternating current that flow (exclusively) in the first output line 5a in which it is not arranged. The second current sensor 14 detects these high frequency components of the alternating current because it is arranged in the return line 9c. net, which is connected to the first output line 5a via the first discharge path 9a. Thus, the high-frequency components of the alternating current are detected in each case, either by the first current sensor 11b as a high-frequency component in the current in the second output line 5b or by the current sensor 14 as high-frequency components in the current that flows from the first output line 5a via the first discharge path 9a and the return line 9c to the intermediate circuit capacitance 3, or by both current sensors.

Of course, the first current sensor 11b can alternatively be arranged in the first output line 5a instead of in the second output line 5b. The distribution of the measurements of the alternating current components between the current sensors 11b and 14 then results analogously to the above description.

This embodiment has advantages over an inverter according to 1a The advantage is that the first current sensor 11b and the second current sensor 14, which is optimized for measuring high-frequency components of the alternating current, are more compact and cheaper than two current sensors arranged in the conventional way in both output lines 5a, 5b, which must each be designed for the simultaneous measurement of the mains frequency and high-frequency components of the alternating current. The current sensor 12 covering both output lines according to 1b is comparatively more complex, since it must be designed for twice the amplitude of the mains frequency component and a correspondingly higher dynamic range than the current sensor 11b according to 2a .

2b shows an embodiment of the inverter 1 according to the invention, in which the second current sensor 14 is arranged in the first discharge path 9a. In this embodiment, the first current sensor 11b detects, as usual, the mains frequency component of the alternating current as well as the high frequency components of the alternating current, provided that these flow (exclusively) through the second output line 5b, in which the first current sensor 11b is arranged, while the second current sensor 14 detects the high frequency components of the alternating current, provided that these flow (exclusively) through the first output line 5a, the discharge path 9a and the return line 9c to the intermediate circuit capacitance 3.

Of course, the current sensors 11b, 14 can alternatively be arranged in the other line, i.e. the current sensor 11b in the first output line 5a and the current sensor 14 in the discharge path 9b connected to the second output line 5b.

This embodiment has advantages over an inverter according to 2a The further advantage is that the current sensors 11b, 14 can be placed individually, thus providing more freedom to optimize the current paths. In particular, the return line 9c can be omitted and the discharge paths 9a, 9b can be connected directly to the end point of the series circuits.

3a shows an embodiment of the inverter 1 according to the invention, which instead of the current sensors 11b and 14 according to 2a only one current sensor 15 covering two measuring points 13b, 16c, which are located at the same positions as the current sensors 11b, 14 according to 2a can be arranged, ie the measuring point 13b in the second output line 5b and the measuring point 16c in the return line 9c. The second output line 5b and the return line 16c are guided through the current sensor 15 in such a way that the current sensor 15 detects the currents flowing at the measuring points 13b, 16c. The current sensor 15 can therefore detect and output a superimposed sum signal of the currents at the measuring points 13b and 16c. The sum signal includes both the mains frequency component of the alternating current that flows along the second output line 5b through the measuring point 13b, and the high frequency components of the alternating current that flow via the first output line 5a, the first discharge path 9a and/or the second discharge path 9b and the return line 9c to the intermediate circuit capacitance 3.

Of course, the measuring point 13b covered by the current sensor 15 can alternatively be arranged in the first output line 5a instead of in the second output line 5b. The total signal detected and output by the current sensor 15 is then composed analogously to the above description.

This embodiment has advantages over an inverter according to 2a The further advantage is that only one current sensor is required, whereby the controller 10 only receives one measurement signal and evaluates it for use in regulating the alternating current.

3b shows an embodiment of the inverter 1 according to the invention, in which the current sensor 15 covers a measuring point 16a in the first discharge path 9a in addition to the measuring point 13b in the second output line 5b. In this embodiment, the current sensor 15 detects a superimposed sum signal which includes both the mains frequency component of the alternating current which flows along the second output line 5b through the measuring point 13b, and the high frequency components of the alternating current which flow via the first output line 5a, the first discharge path 9a and the return line 9c to the intermediate circuit capacitance 3.

Of course, the current sensor 15 can be 3b covered measuring points 13b and 16a can alternatively be arranged in the other line, ie the measuring point 13b in the first output line 5a and the measuring point 16a in the discharge path 9b connected to the second output line 5b.

This embodiment has advantages over an inverter according to 3a The further advantage is that the measuring point 16a may be easier to reach than the measuring point 16c and in particular offers the possibility of dispensing with the return line 9c.

4a shows an embodiment of the inverter 1 according to the invention, which comprises a first current sensor 11a arranged in the first output line 5a and a second current sensor 17, wherein the second current sensor 17 comprises two sub-sensors 17a, 17b, which are arranged in the discharge paths 9a and 9b respectively. The sub-sensors 17a, 17b can in particular comprise shunt resistors, wherein the voltages dropping across the shunt resistors of the sub-sensors 17a, 17b can be combined in particular by means of an operational amplifier such that the current sensor 17 detects and outputs a sum or difference signal of the currents flowing in the discharge paths 9a and 9b. The controller 10 thus receives measurement signals from the first current sensor 11a, in which the mains frequency component of the alternating current flowing in the output line 5a is represented, as well as measurement signals from the current sensor 17, which include the high frequency components of the alternating current flowing in the discharge paths 9a and 9b.

Of course, the first current sensor 11a can be installed instead of in the first output line 5a according to 4a alternatively be arranged in the second output line 5b.

4b shows an embodiment of the inverter 1 according to the invention, which instead of the current sensor 17 comprising shunt resistors according to 4a a current sensor 18 which covers two measuring points 16a and 16b which are arranged in the discharge paths 9a, 9b at the same positions as the partial sensors 17a, 17b of the current sensor 17 according to 4a can be arranged. The current sensor 18 thus detects a sum signal of the currents flowing in the discharge paths 9a and 9b, whereby this sum signal always represents the high-frequency components of the alternating current flowing in the output lines 5a and 5b and thus in the discharge paths 9a and 9b.

Of course, the first current sensor 11a can be installed instead of in the first output line 5a according to 4a and 4b alternatively be arranged in the second output line 5b.

The embodiments according to 4a and 4b Compared to an inverter according to 2a or 2b The further advantage is that the current sensor 11a only has to measure mains frequency components and can therefore be constructed more simply, in particular because a much smaller dynamic range is sufficient.

4c shows an embodiment of the inverter 1 according to the invention, in which, in contrast to the embodiment according to 4b instead of the current sensors 11a and 18, a current sensor 19 is arranged such that it covers three measuring points 13b, 16a and 16b, the measuring point 13b in the second output line 5b being located at a position corresponding to the position of the current sensor 11b according to 2b equivalent position; alternatively and not shown for the sake of clarity, the measuring point in the first output line 5a can be arranged at a position corresponding to the position of the current sensor 11a according to 4b equivalent position. The output line 5a or 5b and the two discharge paths 9a, 9b are guided through the current sensor 19 in such a way that the current sensor 19 detects the currents flowing at the measuring points 13b, 16a and 16b. The current sensor 19 can thereby detect and output a superimposed sum signal of the currents at the measuring points 13b, 16a and 16b. This sum signal includes both the mains frequency component of the alternating current that flows along the first output line 5a or the second output line 5b through the measuring point 13b, and the high frequency components of the alternating current that flow through the discharge paths 9a and 9b. The controller 10 thus receives measurement signals from the current sensor 19, in which both the mains frequency component of the alternating current and the high frequency components of the alternating current are represented.

This embodiment has advantages over an inverter according to 3a The further advantage is that only one current sensor and thus only one signal line to the controller 10 must be present, whereby the measuring points 16a and 16b are easier to reach than the measuring point 16c; in principle, the return line 9c can be dispensed with in this embodiment.

5a shows an embodiment of the inverter 1 according to the invention, in which a first current sensor 20 is arranged in the first output line 5a (not shown) or alternatively in the second output line 5b at a position which differs from the embodiment according to 4b on a side facing away from bridge circuit 2 a connection point of the output line 5a or 5b with the associated discharge path 9a or 9b. At this position in the output line 5a or 5b, the mains frequency portion of the alternating current flows largely exclusively, since the high frequency portions of the alternating current flow via the discharge paths 9a, 9b and the return line 9c before they reach the position of the current sensor 20. In addition, the inverter 1 comprises according to 5a one already in connection with the 4a described current sensor 17, which detects and outputs a sum signal of the currents flowing in the discharge paths 9a and 9b by means of the partial sensors 17a, 17b comprising shunt resistors and an operational amplifier. The controller 10 thus receives measurement signals from the first current sensor 20, in which the mains frequency component of the alternating current flowing in the output line 5a or 5b is represented, as well as measurement signals from the current sensor 17, which include the high frequency components of the alternating current flowing in the output lines 5a, 5b and thus in the discharge paths 9a and 9b.

As an alternative to the current sensor 17 in the discharge paths 9a, 9b, a current sensor 14 can be arranged in the return line 9c in order to detect the high-frequency components of the alternating current flowing in the output lines 5a, 5b and thus in the discharge paths 9a and 9b.

This embodiment has advantages over an inverter according to 4a the further advantage that the current paths for the high-frequency components that flow via the loops comprising the output lines 5a, 5b, the discharge paths 9a, 9b and possibly the return line 9c can be minimized, in particular to optimize electromagnetic compatibility, without a current sensor for the mains frequency component having to be arranged within these loops. In addition, the respective part of the output lines 5a, 5b, which is located on a side of the connection point facing away from the bridge circuit 2 with the respective associated discharge path 9a or 9b, is easier to reach than a position within the said loops.

5b shows an embodiment of the inverter 1 according to the invention, in which, in contrast to the embodiment according to 5a instead of the current sensors 20 and 17, a current sensor 22 is arranged such that it covers three measuring points 21, 16a and 16b, the measuring point 21 in the second output line 5b being at the same position as the current sensor 20 according to 4b can be arranged, ie the measuring point 21 of the current sensor 22 is located on a side of the connection point of the second output line 5b with the second discharge path 9b facing away from the bridge circuit 2. The second output line 5b and the two discharge paths 9a and 9b are guided through the current sensor 22 in such a way that the current sensor 22 detects the currents flowing at the measuring points 21, 16a and 16b. The current sensor 22 can therefore detect and output a superimposed sum signal of the currents at the measuring points 21, 16a and 16b. This sum signal includes the mains frequency component of the alternating current that flows along the second output line 5b through the measuring point 21 and the high frequency components of the alternating current that flow along the discharge paths 9a and 9b through the measuring points 16a and 16b. The controller 10 thus receives measurement signals from the current sensor 22, in which both the mains frequency component of the alternating current and the high frequency components of the alternating current are represented.

Of course, the measuring point 21 can alternatively be arranged in the first output line 5a instead of in the second output line 5b.

This embodiment has advantages over an inverter according to 5a The further advantage is that only one current sensor and thus only one signal line to the control unit 10 is required. In addition, the measuring point 21 is easier to reach than the measuring point 13b according to 3 or 4c , especially if the above-mentioned current paths of the high-frequency components have been spatially optimized.

5c shows an embodiment of the inverter 1 according to the invention, which has a current sensor 23, wherein the current sensor 23 covers two measuring points 21 and 16c. The measuring point 21 is as in 5b in the second output line 5b on a side of the connection point of the second output line 5b with the second discharge path 9b facing away from the bridge circuit 2, while the measuring point 16c is arranged in the return line 9c. The second output line 5b and the return line 16c are guided through the current sensor 23 in such a way that the current sensor 23 detects the currents flowing at the measuring points 21 and 16c, and the current sensor can detect and output a superimposed sum signal of the currents at the measuring points 21 and 16c. The sum signal includes both the mains frequency component of the alternating current that flows along the second output line 5b through the measuring point 21, and the high frequency components of the alternating current that flow via the output lines 5a, 5b, the discharge paths 9a, 9b and the return line 9c to the intermediate circuit capacitance 3.

Of course, the measuring point 21 covered by the current sensor 23 can alternatively be located in the first output line 5b instead of in the second output line 5b. output line 5a may be arranged on a side of the connection point of the first output line 5a with the first discharge path 9a facing away from the bridge circuit 2.

In this embodiment, the measuring point 21 is easier to reach than the measuring point 13b according to 3 or 4c , especially if the above-mentioned current paths of the high-frequency components have been spatially optimized.

Of course, the partial sensors 17a and 17b of the current sensor 17 can be arranged according to 4a and 5a Alternatively, they can be designed as two independent current sensors and transmit their measured values separately to the control unit 10.

The embodiments according to 2a , 2b , 4a , 5a have the further common advantage that the current sensor 14 or the partial sensors 17a, 17b can be designed as shunt resistors and thus much simpler and more cost-effective than magnetic current transformers.

list of reference symbols

1

inverter

2

bridge circuit

3

intermediate circuit capacitance

4

DC connection

5

AC power connection

5a, 5b

output lines

6

filter inductance

7

output filter

8

filter capacity

9a, 9b

discharge paths

9c

return line

10

control unit

11a, 11b

current sensors

12

current sensor

13a, 13b

measuring points

14, 15

current sensors

16a, 16b, 16c

measuring points

17

current sensor

17a, 17b

partial sensors

18, 19, 20

current sensors

21

measuring point

22, 23

current sensor

Claims (17)

Inverter (1) with a bridge circuit (2) which has two half-bridges, each with two semiconductor switches connected in series, wherein the end points of the series circuits are each connected to direct current connections (4) of an input-side intermediate circuit capacitance (3) and the center points of the series circuits are connected to output lines (5a, 5b) for connection to an alternating voltage network, wherein the output lines (5a, 5b) are each connected to one of the end points of the series circuit via a discharge path (9a, 9b) comprising a filter capacitance (8), and wherein the inverter (1) has a control unit (10) which is designed to generate a clocked control of the semiconductor switches of the bridge circuit (2) depending on an alternating current measured on the output side of the bridge circuit (2), wherein the control unit (10) is connected to at least one current sensor (11a, 11b, 12, 14, 15, 17, 18, 19, 20, 22, 23) for measuring the alternating current, characterized in that the alternating current measured on the output side of the bridge circuit (2) is detected at at least two measuring points (13a, 13b, 16a, 16b, 16c, 21), wherein a first measuring point (13a, 13b, 21) is arranged in one of the output lines (5a, 5b) and a second measuring point (16a, 16b, 16c) is arranged in one of the discharge paths (9a, 9b) or in a common return line (9c) to the end point of the series connection, wherein a measuring point (13a, 13b, 21) for measuring a mains frequency portion of the alternating current is arranged in only one of the output lines (5a, 5b), while the other output line (5a, 5b) is free of measuring points (13a, 13b, 21) for measuring alternating current. Inverter (1) after claim 1 , characterized in that the first measuring point (13a, 13b) is arranged in one of the output lines (5a, 5b) and the second measuring point (16b, 16a) is arranged in the discharge path (9b, 9a) connected to the other output line (5b, 5a). Inverter (1) after claim 1 or 2 , characterized in that the current sensor (15, 19, 22, 23) is designed to detect a superimposed sum signal of the currents flowing at the first measuring point (13a, 13b, 21) and at the second measuring point (16a, 16b, 16c). Inverter (1) according to one of claims 1 to 3, characterized in that the current sensor (19, 22) is designed to detect a combination of measured values of the currents flowing at the first measuring point (13a, 13b, 21), at the second measuring point (16a, 16b) and at a third measuring point (16b, 16a), wherein the second measuring point (16a, 16b) is arranged in one of the discharge paths (9a, 9b) and the third measuring point (16b, 16a) is arranged in the other discharge path (9b, 9a). Inverter (1) after claim 1 , characterized in that the inverter (1) comprises a first current sensor (11a, 11b, 20) and a second current sensor (14, 17, 18), wherein the first current sensor (11a, 11b, 20) detects a current flowing at the first measuring point (13a, 13b, 21) and the second current sensor (14, 17, 18) detects a current flowing at the second measuring point (16a, 16b, 16c). Inverter (1) after claim 4 or 5 , characterized in that the second current sensor (17, 18) is designed to detect a superimposed sum signal of the currents flowing at the second measuring point (16a, 16b) and at a third measuring point (16b, 16a), wherein the second measuring point (16a, 16b) is arranged in one of the discharge paths (9a, 9b) and the third measuring point (16b, 16a) is arranged in the other discharge path (9b, 9a). Inverter (1) according to one of the preceding claims, characterized in that the current sensor (15, 19, 22, 23) or the current sensors (11a, 11b, 14, 18, 20) are designed as magnetic current transformers. Inverter (1) according to one of the Claims 5 and 6 , characterized in that the second current sensor (14, 17) comprises a shunt resistor for current measurement. Inverter (1) after claim 8 characterized in that a shunt resistor is arranged in each of the two discharge paths (9a, 9b), the shunts being arranged between the common return line (9c) and the respective filter capacitance (8), and voltages at capacitance-side terminals of the shunt resistors being combined by means of a differential amplifier to form an output signal of the second current sensor (17). Inverter (1) according to one of the preceding claims, characterized in that the first measuring point (21) is arranged at a position in one of the output lines (5a, 5b) which is arranged on a side of the connection of the respective discharge path (9a, 9b) to this output line (5a, 5b) facing away from the bridge circuit (2). Method for operating an inverter (1) according to the generic term of claim 1 , characterized in that the semiconductor switches of the bridge circuit (2) are controlled by means of a unipolar clock, wherein the alternating current flowing on the output side of the bridge circuit (2) is detected at at least two measuring points (13a, 13b, 16a, 16b, 16c, 21), wherein a first measuring point (13a, 13b, 21) is arranged in one of the output lines (5a, 5b) and a second measuring point (16a, 16b, 16c) is arranged in one of the discharge paths (9a, 9b) or in the return line (9c), wherein a measuring point (13a, 13b, 21) is arranged in only one of the output lines (5a, 5b), while the other output line (5a, 5b) is free of measuring points (13a, 13b, 21) for measuring the alternating current. procedure according to claim 11 , characterized in that a mains frequency component of the alternating current is measured at the first measuring point (13a, 13b, 21) and high frequency components of the alternating current are measured at the second measuring point (16a, 16b, 16c). procedure according to claim 11 or 12 , characterized in that the measured values recorded at the first measuring point (13a, 13b, 21) and those at the second measuring point (16a, 16b, 16c) are transmitted separately to the controller (10). Method according to one of the Claims 11 until 13 , characterized in that the measured values recorded at the first measuring point (13a, 13b) comprise the mains frequency component of the alternating current and high-frequency components of the alternating current in one half-wave of the alternating current, and that the measured values recorded at the second measuring point (16a, 16b, 16c) comprise high-frequency components of the alternating current in the other half-wave of the alternating current. Method according to one of the Claims 11 until 13 , characterized in that the measured values recorded at the first measuring point (21) exclusively comprise the mains frequency component of the alternating current, in that the first measuring point (21) is arranged at a position in one of the output lines (5a, 5b) which is located on a side of the connection of the respective discharge path (9a, 9b) to this output line (5a, 5b) facing away from the bridge circuit (2), and in that the measured values recorded at the second measuring point (16c) comprise high-frequency components of the alternating current in both half-waves of the alternating current. Method according to one of the Claims 11 until 13 , characterized in that the measured values recorded at the first measuring point (21) by a first current sensor (20) comprise exclusively the mains frequency component of the alternating current, in that the first measuring point (21) is arranged at a position in one of the output lines (5a, 5b) which is on a side facing away from the bridge circuit (2) of the connection of the respective discharge path (9a, 9b) to this output line (5a, 5b), and that a second current sensor (14, 17, 18) detects the high-frequency components of the alternating current flowing via the discharge paths (9a, 9b) and transmits them to the control (10). procedure according to claim 11 or 12 , characterized in that the currents flowing at the first measuring point (13a, 13b, 21), at the second measuring point (16a, 16b, 16c) and optionally at the third measuring point (16b, 16a) are detected by means of a common current sensor (15, 19, 22, 23) and transmitted to the controller (10) as a superimposed sum signal.

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